1. Field of the Invention
The present invention generally relates to semiconductor devices and, more particularly, to a semiconductor device having external connection terminals on a side surface thereof.
2. Description of the Related Art
In recent years, miniaturization of electronic equipment has progressed, and semiconductor devices used in the electronic equipment has been also miniaturized. As a structure of such a miniaturized semiconductor device, a chip size package (CSP) structure has become popular. In a semiconductor device having the CSP structure, a semiconductor element is fixed on an interposer, and electrodes of the semiconductor element are connected to terminals of the interposer by wire bonding. Protruding electrodes such as solder balls are provided to a lower surface of the interposer as external connection terminals. Accordingly, the package size of the semiconductor device having the CSP structure is much smaller than a conventional lead frame type semiconductor device.
Additionally, a CSP structure, which does not use an interposer, has been suggested. In such a CSP structure, a semiconductor element is not mounted on an interposer, and all wirings and external connection terminals are formed on the semiconductor element. Since such a CSP structure has been achieved, a two-dimensional size of semiconductor devices having the CSP structure has reached their critical limit.
As mentioned above, the two-dimensional miniaturization of the semiconductor devices has reached their limit since they have reached their real chip size. Accordingly, in order to mount the semiconductor elements with further increased density, miniaturization of their mounting area is not needed but miniaturization of their volume is needed. Accordingly, it is desired to develop a stacking structure having a simple structure in which a plurality of semiconductor elements or a plurality of semiconductor devices can be stacked in a three-dimensional state.
When a plurality of semiconductor elements, each of which has a surface on which a plurality of electrodes are formed, are stacked, the surface of each of the semiconductor elements must be covered by an insulating layer so as to stack another semiconductor element thereon. Accordingly, it is an important issue on how to draw out and make a connection with the electrodes of each semiconductor elements.
It is a general object of the present invention to provide an improved and useful semiconductor device in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a semiconductor element stacking structure in which each electrode of each of stacked semiconductor elements can be drawn out with a simple structure.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a semiconductor element stacking structure comprising:
a plurality of semiconductor elements arranged in a stacked state, each of the semiconductor elements having a circuit forming surface on which electrodes are formed;
a resin layer formed on the circuit forming surface of each of the semiconductor elements, the resin layer having an outer configuration the same as that of each of the semiconductor elements; and
a plurality of bonding wires embedded in the resin layer, one end of each of the bonding wires being connected to respective one of the electrodes and the other end of each of the bonding wires being exposed on a side surface of the resin layer.
According to the above-mentioned invention, electrical connection with each of the semiconductor elements can be achieved by using the bonding wires exposed on the side surface of the resin layer as external connection electrodes. That is, each of the bonding wires having the exposed end is connected to a corresponding one of the electrodes of each of the semiconductor elements. Accordingly, the external connection electrode can be formed on the exposed end of each of the bonding wires. Thereby, the electrical connection with each of the semiconductor elements can be achieved by the external connection terminal formed on the side surface of the semiconductor element stacking structure even if the semiconductor elements are stacked.
In the semiconductor element stacking structure according to the above-mentioned invention, the exposed ends of the bonding wires may be aligned along a line separated from the circuit forming surface of corresponding one of the semiconductor elements by a predetermined distance.
Accordingly, when the external connection terminals are formed on the exposed ends of the bonding wires, the external connection terminals and the circuit forming surface are prevented from short-circuiting since each of the exposed ends of the bonding wires is separated by a predetermined distance from the circuit forming surface of the corresponding semiconductor element.
The exposed ends of the bonding wires may be aligned along a plurality of lines separated from the circuit forming surface of corresponding one of the semiconductor elements by different distances, respectively. Accordingly, even if the pitch of the electrodes of the semiconductor element is small and a distance between the adjacent bonding wires in a vertical direction is small, the distance of the adjacent bonding wires can be increased by a distance in a vertical direction. More specifically, the exposed ends of the bonding wires may be aligned along a first line and a second line, the first line being separated from the circuit forming surface of the corresponding one of the semiconductor elements by a first predetermined distance, the second line being separated from the circuit forming surface of the corresponding one of the semiconductor elements by a second predetermined distance, the exposed ends of the bonding wires being alternately arranged so that one of the exposed ends is positioned on the first line and another exposed ends adjacent to the one of the exposed ends is positioned the second line.
Additionally, a protruding electrode may be provided on each of the exposed ends of the bonding wires. For example, the protruding electrodes can be easily formed by stud bumps. Additionally, the corresponding electrodes of the semiconductor elements can be connected by connecting the protruding electrodes aligned in a stacking direction by bonding wires.
Additionally, protruding electrodes may be provided on a surface of a resin layer covering the circuit forming surface of a lowermost semiconductor element from among the stacked semiconductor elements, the protruding electrodes being connected to electrodes of the semiconductor elements. Accordingly, in a case in which the stacked semiconductor elements are the same kind and the electrode arrangement is the same, the protruding electrodes formed on the side surface of the semiconductor element stacking structure can be used as electrode for connecting the corresponding electrodes of the semiconductor elements, and the protruding electrodes provided on the surface of the resin layer covering the circuit forming surface of the lowermost semiconductor elements can be used as external connection terminals.
Additionally, a wiring board may be mounted on a side surface on which the protruding electrodes provided to the exposed ends are formed so that the protruding electrodes are connected to each other by wirings of the wiring board. Accordingly, the corresponding electrodes of the semiconductor elements can be connected to each other by easily connecting the protruding electrodes by the wiring board.
Additionally, another semiconductor element may be mounted on a side surface on which the protruding electrodes provided to the exposed ends are formed. That is, another semiconductor element can be easily mounted by using the protruding electrodes provided on the exposed ends of the bonding wires. Thus, the number of semiconductor elements can be increased. Additionally, a different kind of semiconductor element can be added to the semiconductor element stacking structure.
Additionally, there is provided according to another aspect of the present invention a semiconductor device having a plurality of stacked semiconductor elements, comprising:
a semiconductor element stacking structure comprising:
a plurality of semiconductor elements arranged in a stacked state, each of the semiconductor elements having a circuit forming surface on which electrodes are formed;
a resin layer formed on the circuit forming surface of each of the semiconductor elements, the resin layer having an outer configuration the same as that of each of the semiconductor elements;
a plurality of bonding wires embedded in the resin layer, one end of the each of the bonding wires being connected to respective one of the electrodes and the other end of each of the bonding wires being exposed on a side surface of the resin layer; and
a plurality of protruding electrodes provided on the respective exposed ends of the bonding wires;
a wiring board provided over a bottom surface and side surfaces of the semiconductor element stacking structure;
protruding terminals connected to the respective protruding electrodes provided on the semiconductor element stacking structure through the wiring board, the protruding terminals being provided on a side of the wiring board opposite to, the semiconductor element stacking structure.
According to the above-mentioned invention, since the electrodes of the semiconductor elements are connected to each other by the wiring board and the external connection terminals such as solder balls are formed on the wiring board, the surface mountable semiconductor device can be easily formed.
In the above-mentioned invention, the wiring board may comprise a bottom part covering a bottom surface of the semiconductor element stacking structure and a side part covering a side surface on which the protruding electrodes are formed, and the protruding terminals are provided on the bottom part of the wiring board. Additionally, the wiring board may comprise a bottom part covering a bottom surface of the semiconductor element stacking structure and a side part covering a side surface on which the protruding electrodes are formed, and the protruding terminals are provided on the side part of the wiring board.
Additionally, there is provided according to another aspect of the present invention a semiconductor device having a plurality of stacked semiconductor elements, comprising:
a semiconductor element stacking structure comprising:
a plurality of semiconductor elements arranged in a stacked state, each of the semiconductor elements having a circuit forming surface on which electrodes are formed;
a resin layer formed on the circuit forming surface of each of the semiconductor elements, the resin layer having an outer configuration the same as that of each of the semiconductor elements;
a plurality of bonding wires embedded in the resin layer, one end of the each of the bonding wires being connected to respective one of the electrodes and the other end of each of the bonding wires being exposed on a side surface of the resin layer; and
a plurality of protruding electrodes provided on the respective exposed ends of the bonding wires,
wherein protruding electrodes are provided on a surface of a resin layer covering the circuit forming surface of a lowermost semiconductor element from among the stacked semiconductor elements, the protruding electrodes being connected to electrodes of the semiconductor elements; and the protruding electrodes aligned along a line extending in a stacking direction from among the protruding electrodes provided on the exposed ends of the bonding wires are connected by bonding wires to each other;
a wiring board provided opposite to a surface of a resin layer covering the circuit forming surface of a lowermost semiconductor element;
a seal resin encapsulating the semiconductor element stacking structure on the wiring board; and
protruding terminals connected to the respective protruding electrodes provided on the surface of the resin layer covering the circuit forming surface of the lowermost semiconductor element in the semiconductor element stacking structure.
According to the above-mentioned invention, the electrodes of the semiconductor elements are connected to the protruding electrodes provided on the surface of the resin layer covering the circuit forming surface of the lowermost semiconductor element. Thus, by treating the semiconductor element stacking structure as a single semiconductor element, a semiconductor device having a plurality of semiconductor elements can be easily formed. That is, the semiconductor element stacking structure is mounted on one side of the wiring board and encapsulated by the seal resin, and the protruding terminals such as solder balls can be formed on the opposite side of the wiring board. Thereby, a semiconductor device having a plurality of stacked semiconductor elements can be easily formed.
Additionally, there is provided according to another aspect of the present invention a manufacturing method of a semiconductor element stacking structure, comprising the steps of:
preparing a plurality of semiconductor substrates each of which having a plurality of semiconductor elements;
connecting by bonding wires corresponding electrodes of adjacent semiconductor elements to each other so that the bonding wires extend over boundaries between the adjacent semiconductor elements;
forming a resin layer on a circuit forming surface of each of the semiconductor substrates so as to embed the bonding wires in the resin layer, and stacking the semiconductor substrates so as to integrate the semiconductor substrates with each other; and
cutting the semiconductor substrates and the resin layers together along the boundaries of the semiconductor elements.
According to the above-mentioned invention, each of the bonding wires is formed in an arch-like shape which extends over the boundary between the adjacent semiconductor elements. Accordingly, each of the bonding wires is cut in the middle thereof when the wafer is cut to individualize the semiconductor elements, and a cut end of each of the bonding wires is exposed on the side surface of the resin layer. Since the end opposite to the cut end of each of the bonding wires is connected to the corresponding one of the electrodes of the corresponding semiconductor elements, an external connection terminal can be formed on the cut end of each of the bonding wires. Thereby, electrical connection with each of the semiconductor elements can be achieved by the external connection terminals formed on the side surface even if the semiconductor elements are stacked.
Additionally, the step of connecting may include the step of connecting the bonding wires so that a part of each of the bonding wires above the boundaries is parallel to the circuit forming surface of each of the semiconductor substrates over a predetermined range. Accordingly, each of the bonding wires in the vicinity of a part to be cut can be separated from the circuit forming surface of the corresponding semiconductor element by a constant distance. Thus, the cut end of each of the bonding wires can be maintained at a constant distance from the circuit forming surface even if the cutting line is slightly offset.
Other objects, features and advantages of the present invention will become more apparent from the following descriptions when read in conjunction with the accompanying drawings.